J. Chem. Eng. Data 1981, 26, 13-16
Literature Cited (1) Pher, K. S.; Lippmann, D. 2.; Curl, R. F., Jr.; Hugglns, C. M.; Peterson, E. D. J. Am. Chem. Soc. 1955, 77, 3433. (2) Reid, R. C.; Prausnh, J. M.; Sherwood, T. K. “The Propertles of Gases and Liquids”, 3rd ed.;McGraw-Hill: New York, 1977.
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(3) Wleczorek, S. A.; Kobayashl, R. J. Chem. €ng. Date 1980, 25, 302. (4) Wleczorek, S. A.; Kobayashi, R. J. Chem. Eng. Date, prevlous paper in this Issue. Received for revlew June 30, 1980. Accepted October 17, 1980. The Electric Power Research Instltute provided financial support for this work.
Densities of Molten K2S207-KHS04and K2S207-KHS04-V205 Nlels Holger Hansen” and Nlels J. Bjerrum” The Technical Universiiy of Denmark, Chemistry Depafiment A, DK-2800 Lyngby, Denmark
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Densities of the molten salt systems K,S20,-KHS04 and KZSz0,-KHSO4-VzO5were measured by using the automated float method. Ten different compositions of the K2S20,-KHS04 system were measured. The obtained densRies were fitted to equations of the form p = A ( X ) B ( X ) ( t 400). A ( X ) and B ( X ) were again fitted by polynomials of the mole fraction, Xwso,, in each of the compo!3ition ranges 0.0000 I XKHw4 I0.5000, 0.5000 I XKHm4 I 1.0000, and 0.0000 I Xww4 I 1.0000. Furthermore, all the measured data In each range were fitted to equations of the form p = X,,“A# ( ~ o m B , 4 ” ’ t) ( 400). It was shown that a linear relatlonship exists between molar volume at 400 OC and Xww4 at ail composltions. Two different composltions of the KZSz0,-KHSO4-V,O, system were measured. The observed densities were at each composition fltted to a B(Xl,Xz)( 1 linear equation of the form p = A ( X , , X , ) 400), where X 1 and X z are Xvf16and Xww4, respectively. Finally all the measured data for this system were fitted to the equation p = A BX2 CXz2 ( D EX, F X s z ) X 4 t 400).
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The molten K2S207-KHS04system plays a major role as solvent for various vanadium(V) and vanadium(1V) complexes during the catalytic conversion of SO2 to SO3 for the manufacture of sulfuric acid. As part of a larger investigation ( 7-3) of the catalytic vanadium oxide-pyrosulfate melts, the present paper supplies density data for the K2S207-KHS04system in the whole composition range 0.0000 I XKHS04 I 1.0000 and for the K2S207-KHS04-V205 at compositions around X-, = 0.6. The method employed is the previously described “automated float method” for determination of densities of molten salts (4, 5). This method is very well suited for the present systems, which at the employed temperatures have high vapor pressures. Especially the pure molten KHS04 is believed to exert a high vapor pressure at higher temperatures. One of the quartz cuvettes containing 100% KHS04 broke when the temperature reached 430 OC possibly due to the internal pressure. The high pressure Is probably the reason that only measurements of the density of molten KHS04 at temperatures very close to the meltlng point have been performed (6). The melts containing V2O5 are furthermore very dark colored, thus making visual observations of floats impossible. Experlmental Section The densities were measured by the automated float method (4, 5). The method is based on magnetic detection of quartz floats with iron cores, as they pass a differential transformer. 0021-956a/ai 11726-0013$01 .oo/o
The furnace and its regulation have been described In detail previously (4). Passage temperatures were detected by piatinum resistance thermometers (from Degussa) and by chromel-alumel thermocouples (from Pyrotenax) which were calibrated at the freezing points of pure (99.99%) zinc and lead to within f0.5 OC. K2S2O7 was made by thermal dissociation of K2S208(7) (Merck, Pro Analysi) in a stream of pure N2 in order to avoid contamination by H20. The synthesized potassium pyrosulfate was sealed under vacuum into Pyrex ampules and stored in a glovebox. I t is important to ensure that the hygroscopic potassium pyrosulfate is kept out of contact with atmospheric air-a commercial analytical-grade K&O7 (Riedelde Haen) was shown by Raman spectroscopy to consist of more than 60 mol % KHS04( 7). By weighing it was determined that K2S2O7 did not give off any SO3 at the employed dissociation temperature (290 “C). KHS04(Merck, Pro Analysl) was dried at 110 O C in 3 days and stored in a glovebox. V2O5 (Merck, Extra Pure) was recrystallized under vacuum in a quartz ampule by quick heating to just above the melting point (658 OC), followed by slow cooling. All handling of the solid salts was performed in a nitrogenfilled glovebox with a measured water content of -5 ppm and continuous gas purification by forced recirculation through external molecular sieves. Results The experimental densities and temperatures of the K2S207-KHS04system are given in Table I. The densities of the used floats are calculated on the basis of 8-10 determinations at room temperature and corrected for the thermal expansion of quartz at the measured temperature. In Table I1 the results for the K2S207-KHS04-V205are given In a similar way. The standard deviations of the measured temperatures are calculated in accordance with the procedure described previously (4). In Table I11 the measured densities for the K2S207-KHS04 system are at each composition expressed by A ( X ) and B(X), where p = A ( X ) B(X)(t - 400). p is the density in g/cm3, A ( X ) is the density at the composition XKW, at 400 OC, B(X) is the density change per degree at the composition X, and t i s the temperature in OC. As described previously (5) this expression gives a more satisfactory representation of the measured data than the usually employed equation p = A ( X ) B(X)t. In Table I V the results for the K2S20,-KHS04-V205 are given analogously by A(Xl,X2)and B(X,,X2)( X , = X-,, x2 = Xvp,).
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0 1981 American
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14 Journal of Chemical and Engineering Data, Vol. 26, No. 1, 1981
Table I. Experimental Densities and Temperatures of the Molten K,S, 0,-KHSO, System densities of floats, g/cm3 at 20 "C 1.9697 1.9697 1.9697 2.0019 2.0019 2.0019 2.0019 2.0172 2.01 72 2.01 76 2.01 72 2.01 76 2.0172 2.01 76 2.0176 2.031 7 2.0317 2.031 7 2.0343 2.034 3 2.0343 2.0 34 3 2.0398 2.0398 2.0398 2.0398 2.0504 2.0504 2.0504 2.0504 2.0730 2.0730 2.0730 2.0730 2.0730 2.0744 2.0744 2.0744 2.0744 2.0981 2.1114 2.1114 a
measured temperatures at the given XKHSO,mole fractions, "C
at measd temp
0.0000
0.1000
i s . . 475.8
?-
0.3000
0.4000
0.5000
0.6000
0.7000
0.7750
0.9000
1.0000
4 75.8 (8)a
1.9682 1.9683 1.9684 2.0004 2.0005 2.0006 2.0007 2.0154 562.4(9) 2.0159 2.0159 2.1060 2.1060 2.0161 2.0161 2.0162 2.0301 3.0302 2.0305 2.0327 2.0328 2.0329 2.0331 2.0381 528.5(21) 2.0386 2.0388 2.0389 2.0488 2.0489 2.0490 2.0492 2.0715 2.0716 2.0717 2.0718 2.0719 2.0728 447.0(18) 2.0733 2.0734 2.0735 2.0966 440.7(20) 2.1103 2.1 104
44 1.6(9) 410.8(10) 496.4(5) 4 7 1.O (8) 429.4(9) 395.8(10) 40 7.1(7) 54 1.5(8) 373.3 (8) 506.8(7)
491.1(5) 343.3(6) 473.4(18) 423.5(7)
520.9(11) 485.5(12)
470.0(12) 403.5(11)
51 7.2(8) 482.3(17) 464.3(16) 401.4(11) 375.3(6) 34 2.9 (6) 31 1.1(5) 493.4(9) 459.3(11) 441.4(10) 376.4 (10) 459.4(17) 426.0(25) 408.1(26)
392.1(6) 366.8(21) 343.0(10) 3 25.7 (5) 294.5 (6) 263.5(5) 338.1(7) 31 1.1(8)
0.8.
Table 11. Experimental Densities and Temperatures of the Molten K,S, 0,-KHS0,-V,O, System density of floats, g/cm3 at 20°C
at measd temp
2.001 9 2.01 76 2.0176 2.0317 2.0504 2.0504 2.0730 2.0730 2.1114
2.0004 2.0160 2.0161 2.0303 2.0490 2.0491 2.0717 2.0718 2.1104
measured temperatures at the given mole fractions
XKHSO,: XK,S,O,:
xv,o,:
0.6000 0.4000 0
0.5920 0.3946 0.01 34
0.5734 0.3829 0.0447
471.0(8) 489.0(20) 463.4(8) 442.4(9)
460.8(6) 434.7(6)
41 3.8(8) 398.5(5) 366.8(21) 31 1.1 (8)
379.8(20)
From the molar volumes listed in Table 111, it is observed that for the K2S2OrKHSO4 system a linear relationship between the molar volume at 400 OC and composition exists in the whole I1.0000. This is iiluscomposition range 0.0000 IXKHSO,
Table 111. Linear Density Equations and Molar Volumes of the Molten K,S, 0,-KHSO, Systema mole fraction KHSO,
A(X),b
0.0000 0.1000 0.3000 0.4000 0.5000 0.6000 0.7000 0.7750 0.9000 1.0000
2.1240(3) 2.1119(4) 2.0897(4) 2.0769(6) 2.0669(3) 2.0492(2) 2.0330(3) 2.0212(1) 1.9977(3) 1.9759(4)
g/m'
103B(X),b g/(cm3 deg)
SD, g/cm3
molar vol at 400 "C, cm3/mol
-0.669(3) -0.677(3) -0.691(5) -0.672(9) -0.693(5) -0.687(2) -0.687(12) -0.700(2) -0.715(5) -0.713(4)
0.0002 0.0002 0.0003 0.0006 0.0006 0.0003 0.0007 0.0002 0.0005 0.0004
119.73 114.82 104.74 99.69 94.46 89.50 84.41 80.89 74.08 68.92
For the measured temperature ranges, see Table I. A ( X ) t B ( X ) ( t - 400).
p
=
trated in Figure 1 and indicates that the molten salt system K2S207-KHS04 is ideal. In Figure 2 A ( X ) and B ( X ) are shown as functions of the composibion of the K2S20,-KHSO4 system. Here are shown the best A ( X ) polynomial fitted to the data (by the least-squares
Journal of Chemicaland Engineering Data, Vol. 26, No. 1, 1981 15 Table N. Linear Densitv Eauations and Molar Volumes of the Molten K.S.0.-KHS0.-V.O. mole fraction KHSO, (X,)
0.6000 0.5920 0.5734
mole fraction KaS,O, 0.4000 0.3946 0.3823
Svstem'
mole fraction V,O, (X,)
A(x,,x,),~ dcm3
s/(cm3 deg)
SD,glcm'
0 0.0134 0.0443
2.0492(2) 2.0584(2) 2.0706(2)
-0.687(2) -0.664(4) -0.616(4)
0.0003 0.0003 0.0003
molar vol at 400 "C, cm~lmol
10'B(X,,X,),b
89.50 89.09 88.55
'Forthe measuredtemperatureranges,seeTableII. b ~ = A ( X , , X , ) + B ( X , , X , ) ( f - 4 0 0 ) . Table V. Values of Coefficients in Empirical PolynomiB for Densities ofthe Molten K,S,O,-KHSO, System in Different Composition Ranges 0.5000 < XKHSO,< 1.0000 (n=3,m=l)
0.0000 < XKHSO,< 0.5000 ( n = l , m=l) A, A,
2.12341 -0.11355
2.239 19 -0.574 91 0.608 67 -0.297 20
-0.66859 XX 1 100 .' -0.05379 .'
-0.66088 -0,05278 XX 10.'
A,
A, A4 A< A6 XKHSO,
BO
Flgure 1. Molar volume of the K,S,O,-KHSO, ,,, mole fraction ,X
system at 400 'C vs.
E.
SE,
1.0000 (n=6,m=l) 2.123 96 -0,12279 -0.15256 1.309 99 -3.357 34 3.393 21 -1.21844 -0.66727 XX 10.' IO-> -0.04258 0.0009
0.0006
0.0006
0.0000
